1. Field of the Invention
The present invention relates to photonic crystal (PhC) cavities and more particularly to a novel method for deterministically designing and making a high quality factor, wavelength scale photonic crystal nanobeam cavity. The deterministic method of the present invention can be applied to different material systems and to cavities resonant at different ranges of wavelengths as well.
2. Brief Description of the Related Art
Photonic crystal (PhC) cavities with high quality (Q) factors and wavelength-scale mode volumes are widely applied in fields that range from quantum information processing and nonlinear optics to biomedical sensing. PhC nanobeam cavities (shown in FIG. 1) are based on a strip waveguide 110, with grating sections (dielectric alternations) along the waveguide. These grating sections provide constructive optical interference and confine light. One form of the grating is etched holes 120 along the waveguide, but many different types of gratings can be used.
PhC nanobeam cavities have small footprints and are naturally integrated with optical waveguides. Hence, they are ideal candidates for the realization of densely integrated photonic systems and are suitable for applications ranging from optical interconnects to biochemical sensors.
A nanobeam cavity made of silicon is demonstrated in Foresi et. al., “Photonic bandgap micro-cavity in optical waveguides,” Nature 390, p. 143 (1997). The quality factor, however, was only around 250. The major loss came from scattering due to imperfect design of the grating sections 120.
The design of PhC cavities is typically based on extensive parameter search and optimization, also known as intuitive design. See for example, Y. Akahane, T. Asano, B. S. Song, & S. Noda, Nature 425, 944-947 (2003); B. S. Song, S. Noda, T. Asano, & Y. Akahane, Nature Materials 4, 207-210(2005); S. Tomljenovic-Hanic, C. M. de Sterke, & M. J. Steel, Optics Express 14, 12451-12456 (2006); E. Kuramochi et. al., Appl. Phys. Lett. 88, 041112 (2006); M. Notomi, E. Kuramochi, and H. Taniyama, Optics Express, 16, 11095(2008). The large computational cost, in particular the computation time, needed to perform the simulation of high Q cavities makes such a trial-based method inefficient.
Other methods have been proposed as well. Inverse engineering design, in which the physical structure is optimized by constructing specific target functions and constraints, was proposed in J. M. Geremia, J. Williams & H. Mabuchi, Phys. Rev. E 66, 066606(2002). A design recipe based on the desired field distribution is proposed in D. Englund, I. Fushman & J. Vuckovic, Optics Express 13, 5961-5975 (2005).